Piezo-electric device



June 10, 1930.. w. HAHNEMANN 1,763,515

PIEZO ELECTRIC DEVICE} 7 Filed June 19 1928 WIFE/7140);! War/fer //a/7 ema/m,

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The present invention has for its ohject a device for automatic maintenance of the constancy of the ire uency all electrical os- Eh the help oi the so called ieaoresonators, as have heen emloyed ately in high-irequency engmeermg or. dih'erent urposes. Such crystals are suitable to maintain automatically on a con stant value as desired the frequency at an oscillatory circuit which frequency in consequence of any external influences, is suhject to fluctuations. Difficulties, however, arise in that the crystals employed, with the devices so far in use, were exposed. to high tensions, as they had to be connected 1 in parallel with the entire self-inductance or capacity oil the oscillatory circuit. Q The crystals are, however, extremely sensitive to high tensions, and may easily he destroyed lay them.

in accordance with this present invention the crystals are only. coupled with a part (a fractional portion) oi the inductance or capacity oi the oscillatory circuit; This ensures that the crystal will only he exvposed to a portion oi the full voltage prevailing in the syntonization circuit.

The invention is more fully set forth by reference to the accompanying drawings which show diagrammatically some practical embodiments of the invention.

Fig. l isa high frequency circuit having a piezoelectric crystal device associated therewith in accordance with this invention.

Fig. 2 is a similar circuit having the crystal connectcdin a different way, and

Fig; 3 is a combination of the arrange ments according to Figs. 1 and 2, employing two crysta s, "whereby a combined and improved action as compared to the arrangements of Figs. 1 and 2 is obtained. Sumilari reference characters refer to similar elements in the individual figures.

Referring to the drawings; L is an inductance of an oscillatory circuit and C in series with C forms the capacity of the circuit.' This circuit may be the oscillatory circuit of a discharge device or a vacuum tube generator G producing a-negative resistance characteristic hetween two oi its electrodes which are connected to the points a and h o'ithe circuit shown in the drawing. As is well known, in this case electric oscillations will he maintained in the circuit L, C and G having a frequency determined by the natural frequency olthe circuit. As practical experiments have shown and as may he proved by theoretical analysis, the frequency or? the oscillations may he furthermore effected loy the value of the negative resistance of the tuhe, i. e., steepness of the negative slope of its resistance characteristic. This latter is suhject itself to variations due to the variations of heating current, anode voltage or other su ply sources. Therefore, these variations will produce corresponding frequency changes. lln my invention l provide a piezoelectric device to compensate for these variations and'to minimize these frequency changes.

Furthermore, the capacities C and 6 may he themselves suhject to variations. For example, one of them may he the am tenna capacity which varies its value on account of mechanical movements, such as swinging hy the wind, or on account of changes in the surrounding objects, atmosphere, etc.

These capacity changes of the-antenna are oi great disadvantage, especially in the case of very short waves in that minute deviations from a normal value will cause corresponding iirequency changes of the waves radiated and consequent detuning and distortion of signals. According to the invention, a piano electric crystal K is placed parallel to the capacity (3 The capacities C and C are of such 'difi'ering value that the larger amount of voltage drop is taken up by the capacity (3 wlnch has a small cepacityvalue as compared to that of the capacity C Thus, the voltage drop across C is low enough to secure a reliable operation of the crystal K If the crystal has a natural frequency f equal to the desired frequency f to be maintained, it will have no influence under normal conditions and will act only as a high resistance. If, however, the frequency (f) increases, even. by

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till l=l 0 2 51+? where K is the caplacit'ative impedance 'of 3 crystal K This s ows that the resultant capacity is decreased by the comparatively large influence of K so that there is a tendency to maintain the original fre que ncy.- In case the frequency is decreased similar consideration would show that the crystal acts in the o posite direction tending to maintain the re uency at its'normal'value. (See Cady, Vol. V age' 83, Proceedings Institute of Radio ngineers, 1922.)

Referring to Fig. 2. the same effect is obtained as in Fig. 1 by placing a crystal K in parallel with a suitable 1piart (fractional portiorr) of theinductance of the oscillatory circuit. The crystal is connected galvanically, as in the drawing, or inductively by an induction coil. {If in this case the frequency 'f decreases with respect to normal frequency f of the crystal to be maintained,

then the crystal K will present an impedance equivalent to that of an inductance whereby the resultant inductance L is decreased, i. e.,,' the natural frequency increased. Thus there is a tendency to maintain' the original frequency.

According to the arrangement of Fig. 3, which is a. combination of Figs. 1 and 2, both crystals K; and K are provided .whereby a combined and improved action is ob tained, as may be readily understood. It is not essential, of course, that the piezo elec tric device be connected in the s cificmanner therein shown in the drawlngs, but it may be arranged in any suitable manner to effect the'natural constantsof theoscillatory circuit in order to bring aboutthe efiect described without de arting from the scope "of the present invention as stated in theappended claims.

. he circuit shown in the drawing may repsent the oscillatory circuit of any circuit arrangement and is not restricted to the arrangements specifically referred to above. It may, for instance,be the anode' circuit of. a self-oscillating vacuum tube oscillator using a reaction between anode and control -signature.

maintained in said circuit, andlfilaced in parallel relationship to a fractio part of one of said elements so as to be ex to less than the full. voltage of the circuitand adapted to vary its impedance presented to said currents in such a manner as -to com.

pensate for variations of said inductance and capacity elements to maintain the natural frequenc of said circuit.

2. A I frequency electric circuit including in uctance-and capacity and carry-v ing currents having a frequency dependen I, on the natural frequency ofsaid circuit, a

piezo-electric crystal device having a natural frequency equal to the frequency to be maintained in saidcircuit and arranged in parallel with a fractional portion of the capacity in said circuit so as to be ex (1 to less than the full tension of the fu circuit capacity and adapted to change the resultant capacity of the circuit capacity element. and crystal combination in such a manner as to tend to maintain the natural freof said circuit.

eluding inductance and capacity elements and carrying currents having a frequency dependent on the natural frequency of said.

circuit, a piezo-electric crystal'device having a natural frequency equal to the frequency to be maintained in said circuit and laced parallel to a capacity element in the circuit, and a second piezo-electric crystal device placed parallel to an inductance element-in the circuit, said crystals being adapted to change the effect-of said capacity and inductance elements in such a'manner as to tend to maintain the natural frequency of said circuit.

In testimony WALTER HAHNEMANN.

whereof I have aflixed my circuit, in which case the crystal will act to 4. keep constant the frequency of oscillations high-frequency electric circuit in- 

